The objective of this research is to determine the molecular structure of calmodulin, using protein x-ray crystallographic techniques. This calcium-binding protein, which has been sequenced and has a molecular weight of 16,700 daltons, has been crystallized in this laboratory, and work toward the low-resolution structure is in progress. The ultimate goal is the high-resolution (1.8 Angstrom) crystal structure. Calmodulin possesses a high degree of sequence homology to troponin-C and parvalbumin; its structure would provide information about this general class of calcium-binding proteins. In addition, the structure may provide clues to its function as a regulator of numerous enzymes.